Immune defense parameters of wild fish as sensitive biomarkers for ecological risk assessment in shallow sea ecosystems: A case study with wild mullet (Liza haematocheila) in Liaodong Bay.

Abstract

Environmental monitoring is important to the health management of an ecosystem. Biomarkers are particularly relevant because they are direct indicators of any toxic effects on organisms and are cheaper to use compared with chemical indicators, especially for extremely low-level organic contaminants. Fish can be significantly affected by pollutants, given their high trophic levels in aquatic food chains. Their immune function is closely related to their survival. The present study compared immune function-related parameters of wild mullet (Liza haematocheila) samples from low (Jinzhou) and high (Yingkou) polluted sites during the pre-winter (PW) and pre-breeding (PB) periods in Liaodong Bay, to evaluate the effect of water pollution on fish health and to explore potential biomarkers of coast water pollution. Compared with Jinzhou mullet, there was a significantly higher level of hematocrit in Yingkou mullet, but a significantly lower serum lysozyme level (P<0.001), indicating that these fish were immunosuppressed. Significant differences occurred in the spleen between the two site populations. The abnormal: normal fish ratio in Yingkou L. haematochila was significantly higher than that of Jinzhou L. haematochila (2.5 times of that of Jinzhou during PB and nine times during PW). The splenic index of male Yingkou L. haematochila was 47.2% higher than that of Jinzhou L. haematochila in PW (P=0.001). Moreover, histological observations showed that the spleen of the former was more congestive, with increased numbers (39.6% more) of melanomacrophage centers (MMCs) and changes in pigments (hemosiderin 8.3% higher and melanin 29.4% higher), compared with the latter. The splenic MMC area of Yingkou L. haematochila was significantly smaller than that of Jinzhou L. haematochila (P<0.05) in PB, but showed no clear difference in PW (P>0.05). Splenic MMC number was significantly higher in individual Yingkou L. haematochila with abnormal livers compared with normal Yingkou L. haematochila during both sampling periods. The splenic MMC area in abnormal livers was approximately four times those of normal individuals during PB in Yingkou L. haematochila. The number of splenic melanomacrophages (MM) in abnormal livers was approximately nine times those of the normal livers during PW. There were also differences in pigments in normal Yingkou individuals compared with normal Jinzhou samples during PW (melanin 29.4% higher and hemosiderin 8.3% higher). Based on these results, we suggest that serum lysozyme activity, splenic MM number and MMC (both number and area), and melanin of local fish have potential as sensitive biomarkers for the assessment of coastal water pollution.